Interpretive Summary: An index to maximize profit from selection of Holstein sires for use in Mexican herds was developed. The index consists of weights for the predicted transmitting ability for milk yield (the part of the bull's genetic value expressed in his daughter's lactations) and for the cost per dose of the bull's semen. The index was constructed from a model of profit for Mexican herds using random simulation, appropriate biological and economic parameters and equations to convert predicted transmitting abilities for milk production per lactation published in one country to what would be expected in another country, in this case, Mexico. For example, bulls with daughters only in the United States or in Canada can be compared with bulls with daughter production only in Mexico. The index can be used to decide whether a US or a Canadian or a Mexican bull would be most profitable for a herd owner in Mexico. The index equation could be used to promote sale of dairy bull semen from the US (or Canada) to Mexico. First the predicted transmitting ability (PTA) of the US or Canadian bull would be converted to a Mexican PTA (PTA (Mexico, kilograms)) using formulas developed by the USDA. Then the profit index would be used for the appropriate planning horizon. The profit index for a 10-year investment horizon is: 2.15 (milk price/kg) x (PTA (Mexico)) - 19.92 (semen price/dose). The profit index for a 20-year investment horizon is: 5.80 (milk price/kg)xPTA (Mexico) - 32.12 (semen price/dose).

Technical Abstract:
An index to maximizing profit from Holstein sire selection for use in Mexican herds was developed. The index was constructed from a model of profit in Mexican herds, using stochastic simulation, biological and economic parameters and equations to convert predicted genetic differences for milk production from one country to another country. The profit index for 10-year investment horizon period in Mexico was IB10 = 2.14 * milk price per kg * PTA (MEXICO) - 19.92 * semen price per dose. The profit index for 20-year investment period was IB20 = 5.80 * milk price per kg * PTA (MEXICO) - 32.12 * semen price per dose. Aspects related to the application of the index in bulls evaluated in Mexico and other countries are discussed.